This invention relates to ink jet printer devices, including devices which are sometimes called ink-operated mosaic printer devices. More particularly, this invention relates to the piezoelectric drive element assemblies which are commonly used in such devices.
An ink jet printing, droplets of printing liquid or ink are ejected onto paper or other record media by piezoelectric contraction of drive elements which form or surround passages through which the printing liquid flows. A typical drive element comprises a hollow body, such as a piezoceramic tube having external and internal cylindric lateral faces. These faces can be coated or otherwise combined with metal or other conductive material to provide a pair of electrodes for operating the drive element. Upon application of an electrical signal or pulse across the electrodes, as by means of a conventional character generator circuit, there is a mechanical contraction of the piezoceramic tube and this contraction is transmitted to the ink to cause ejection of an ink droplet onto the record media.
Background relating to known piezoelectric drive elements is contained in U.S. Pat. Nos. 3,298,030; 4,158,847; 4,288,799 and 4,323,908; and these U.S. patents are hereby incorporated herein by reference.
The piezoelectric drive elements are normally components of a print head assembly which, for different constructions, can be either stationary or movable with respect to the printer device. A print head assembly can comprise a single piezoelectric drive element or it can comprise multiple elements. Multiple elements can be arranged in a column, in a row or in an array consisting of columns and rows. For example, in printing in variable colors, it is particularly convenient to utilize a movable print head comprising multiple piezoelectric drive elements which are arranged in an array.
By way of illustration, a print head having multiple drive elements may be supplied with three inks each of a different primary color, and a separate column of drive elements may be used for each ink. With such a print head, alphanumeric characters in seven different colors can be printed in a matrix pattern of ink dots. The color of each dot, and therefore the color of each character, would be determined either by using one of the three inks, or by using a combination of two or three of those inks. Combining the inks can produce four additional colors which can be obtained by means of successive passes of the ink jet print head relative to the paper or other record media.
In movable ink jet print heads, which comprise multiple piezoelectric drive elements, it is known to supply the ink by means of reservoirs which are made a part of the print head assembly. The reservoirs will normally maintain the ink supplies as narrow vertical columns of ink which are arranged perpendicular to the direction of the print head movement during printing. The reservoirs are thus constructed to minimize the formation of pressure waves in the ink supply which may be induced by nonuniform movement of the print head. In one known color ink jet print head, as disclosed in German Pat. No. DE/PS 2925812, which is hereby incorporated herein by reference, an example is given of a movable print head comprising three ink supply reservoirs which are arranged in a row for color ink jet printing.
To achieve high rates of printing, as expressed in characters per second, or lines per minute, movable print heads are subjected to high rates of acceleration and deceleration during the printing process. It is accordingly desirable to minimize the mass of movable print heads, in order to minimize the forces necessary to be exerted upon the print heads for high rates of printing.
It is known to produce movable print heads of low mass by casting an epoxy or other suitable resin in a mold. Before the resin is cast, the piezoelectric drive elements are supported within the mold cavity by means of corresponding pins which are part of the mold. The drive elements are slipped onto these pins, and the resin is cast and allowed to harden. The pins are then withdrawn from the resultant cast body, leaving the channels or passages through which the ink is to pass for ejection. This is a known construction method which provides in situ casting of the piezoelectric drive elements in the cast print head while forming passages for the flow of ink which is to be ejected. This method has been disclosed in U.S. Pat. Nos. 4,095,238 and 4,158,847 which are hereby incorporated herein by reference for informational purposes.
In the manufacture of print heads of all types and configurations for ink jet printing, it is desirable to provide a secure and simplified means by which electrical connections are made to the electrodes of the piezoelectric drive elements. It is also desirable to provide a simplified means by which the piezoelectric drive elements can be accurately arranged and mechanically secured within the print head unit, whether the unit be formed by casting or some other process.